Metal Story: Lead (Pb)

投稿日付: 30/ 05/ 2018 - ポスター: VTRiT

Metal Story: Lead (Pb) – The metal that destroyed Rome

That Rome was saved by geese is common knowledge. The good birds noticed the advancing enemy in time to announce his coming in loud piercing cries and warn of the danger. That time the city escaped unharmed: it was destined to fall later. Why did the fall of the once powerful Roman Empire take place? What destroyed Rome?

Some American toxicologists maintain that the end of Rome had been caused by lead poisoning, a result of the use of dishes set in lead and of lead cosmetic paints by the Roman aristocracy. Owing to the systematic poisoning by small doses of lead, the average life span of the Roman patricians was not more than 25 years. People of the lower classes, according to this theory, were not subject to lead poisoning so much because they had no expensive dishes and did not use cosmetics. But on the other hand they too used the famous water main which had once been built by Rome’s slaves and which, as it is well known, had pipes made of lead. People were dying and the empire was going into a decline. It goes without saying that lead was not the only factor responsible for that state of affairs. There were also serious political, social and economic reasons. But still there is a lot of truth in the American theory : the remains of ancient Romans found at archaeological excavation sites contain large quantities of lead.

All soluble compounds of this element are poisonous. It has been found that the water which fed ancient Rome was rich in carbon dioxide. Reacting with lead it forms lead carbonate which readily dissolves in water. Introduced even in minute doses in the human organism lead is retained by it gradually replacing the calcium in the bones and giving rise to chronic diseases.

But the destruction of Rome is not the only crime on the “conscience” of lead. Many “shady dealings” are attributed to it. When the Inquisition was rampant the Jesuits used molten lead as a means of torture and execution. In India even as late as the beginning of the last century a person belonging to a lower caste and caught eavesdropping on Brahmins during the reading of sacred books, intentionally or not, had molten lead poured into his ears (since time immemorial the priests of Babylonia, Egypt, and India had kept their knowledge in deep secrecy in order to be able to exercise power over their people).

Surviving in Venice is the notorious medieaval state prison connected with the Doge’s Palace by the Bridge of Sighs. In the old days the prison’s attic had cells under a lead roof for especially dangerous criminals. In summer the prisoners were scorched by unbearable heat and in winter, they were dying of cold, and their screams of pain could be heard on the Bridge of Sighs.

Since firearms had been invented, lead began to be used for lethal bullets and was the weightiest argument in settling controversies between hostile parties. It was lead that decided the outcomes of major battles and small-time gangster fights.

An impression may be created that lead is a metal the use of which spells nothing but danger and that humanity’s chief concern should be to get rid of this wicked element which has already caused so much misfortune and suffering. But far from attempting to get rid of it, humanity is constantly developing lead production. Of all the nonferrous metals only aluminium, copper and zinc are produced in larger amounts.

Then what is the good side of lead?

History has recorded plenty of examples of nations waging just wars for freedom and independence and being helped by lead in their struggle. In order to be confident of the impregnability of one’s country’s borders it is necessary not only to have mettle but also lead. The military significance of lead is enormous.

There was a dramatic increase in lead production at the beginning of the century when the rapid advance of technology led to the development of motor vehicles, submarines and planes, and to the rise of chemistry and electrical engineering.

Approximately one-third of the world lead production is used for the manufacture of storage batteries, the grids for which are made from an alloy of lead and antimony and the active mass from a mixture of lead and litharge (yellow lead).

The fuel industry is among the major users of lead. Before gasoline is ignited in the engine, it is compressed and the greater the compression the more economical the engine is. But under heavy compression the gasoline detonates without having been ignited. Naturally this cannot be permitted. Tetraethyl (anti-knock) lead was summoned for help. Added to gasoline, this substance (less than 1 gram per ’ litre) prevents detonations, ensuring that the fuel burns evenly, and what is even more important, only when necessary.

Since tetraethyl lead is very poisonous the gasoline containing it is dyed pink to distinguish it from common gasoline. Regretfully, considerable amounts of poison are discharged by motor engines into the atmosphere together with the exhausts. According to scientists at the California Institute of Technology (USA), whole clouds of lead are transported over the heads of residents of big cities (as you see the expression “leaden clouds” can justly be understood as “lead clouds”): in one year nearly 50000 tons of lead formed mainly from the lead anti-knock (this is what 1 gram per litre means!) precipitate over the seas and oceans of the northern hemisphere alone. The “motor-born” lead has even been discovered in Arctic snow. Obviously, tetraethyl lead must be replaced by something else, but it has not been possible so far.

In electrical engineering lead is used as a reliable and adequately elastic sheathing for the cables. Considerable amounts of it also go into various solders.

At chemical and nonferrous metals .plants lead sheathing is used for the inner surface of chambers and towers involved in the production of sulphuric acid and also for pipes, pickling baths and electrolyzers.

The bearing alloys of lead with other metals are employed in many machines and mechanisms. Alloyed with antimony and tin it is included in the composition of the type metal.

In glass and ceramics making lead is essential for the manufacture of cut glass and special glazes. The oxides and salts of lead are indispensable in the varnish-and-paint industry. Lead paints were known in old times too.

Even 3000 years ago people knew how to prepare white lead. The Rhodes island was the biggest exporter of it in those times. The method used to make the paint was not very sophisticated but reliable. A solution of vinegar was poured into a cask, branches of shrubs were arranged over the solution and pieces of lead were put on top. After that the cask was covered tight. Opened after a while, the lead would be found with a white substance — white lead — deposited on its surface. It would be scraped off the metal, packed and taken to other countries.

One day fire broke out on a ship loaded with white lead and moored in the Athens port of Piraeus. The artist Nieias, who happened to be in the vicinity and knew there was paint on the burning ship (and paints were expensive then), went on board wishing to save some casks, even if one. But to his utter amazement, he found that the charred casks contained not white lead but some thick substance of a bright red colour. He seized one and hurried to his workshop where he discovered the contents to be an excellent red paint. Later it was called red lead and was obtained by roasting white lead.

Icons and paintings done in lead paints dim with time but it is enough to wipe them with a weak solution of hydrogen peroxide or vinegar for the paints to look fresh and bright once more. Churchmen knew about it very well and liked to fool believers performing a “miracle” before their eyes and making the icons “come alive”.

Lead compounds are used in medicine as astringents, anticeptics and analgesics. Lead acetate (Goulard water) is known as the sugar of lead for its sweet taste. It must never be forgotten, however, that this “sugar” can cause a bad poisoning.

It is for good reason that protective measures are taken in shops and laboratories where employees work with lead or its compounds. Hygienists and labour safety engineers see to it that the content of lead in the atmosphere should not rise above the permissible level of 0.00001 milligram per litre. Not long ago lead-poisoning was an occupational disease of workers at lead smelters and printing shops. But not any more: improved production technologies and measures ensuring adequate ventilation and dust removal have almost completely ruled out conditions induced by lead poisoning.

Paradoxically though it may seem, lead not only poisons, but also offers protection. Metallic lead has been proved to be one of the most opaque materials for radioactive and X-rays. Try holding a radiologist’s apron or gloves — you will be impressed by their weight: they are made from rubber mixed with lead which traps the extremely dangerous X-rays and protects the organism. The grain of radioactive cobalt used in the cobalt gun to treat malignant tumours is also safely sealed in a lead bulb.

Lead screens are vital in the atomic power industry. Glass containing lead monoxide can also serve as a protection against radioactive radiation. Such glass makes it possible to control the work of the reactor handler of a nuclear installation. The atomic centre in Bucharest is equipped with a porthole made from lead glass one metre thick and weighing more than one and a half tons.

The lead content in the earth’s crust is not so high — thousands of times less than the content of aluminium or iron. Nevertheless, man became familiar with it in very remote times — something like 7000-5000 years B. C. Unlike many other metals, lead has a low melting point (327°C) and occurs in nature in the form of rather unstable chemical compounds. This is why it was sometimes produced by chance.

A case in point is an incident recorded in America when a rich lead deposit was discovered as a result of a forest fire: big lead nuggets were found under the layer of ashes. The fire had “smelted” it from the ore deposited beneath the roots of trees. Very likely that was how the first lead had gotten into hands of our prehistoric ancestors. The lead figurine coming from Egypt and kept in the British Museum is believed to be the oldest sample of lead that has come to us from antiquity. Ancient lead slag heaps are still found in Spain where Phoenicians developed the Rio Tinto lead-and-silver deposit in the third millennium B.C.

In the library of the Assyrian King Ashurbanipal (VII century B.C.) there are copies of Babylonian manuscripts dating approximately to the year 2000 B.C. One of them includes a hymn to the God of Fire : “Oh great God, you melt copper and lead, you purify gold and silver.” During excavations in the city of Ashur archaeologists discovered a lump of lead weighing 400 kilograms. They referred its origin to the year 1 300 B. C.

One of the methods of determining the age of mountain rock and archaeological finds is associated with lead. Most types of rock and minerals contain small amounts of radioactive elements. The natural cycle which has lasted for thousands of years has caused some elements to decay and others to originate. The constant process of transformation that some metals undergo results in the formation of radium which, for its part, also disintegrates, gradually turning into lead. Given the amount of radium contained in a certain rock and the amount of lead formed every year, it is possible to determine the age of the rock. For example, it was found that the coal deposits of the Donets Basin were formed about 300 million years ago.

Traces of ancient lead workings have been discovered in the Soviet Union in Altai, the Transbaikal area, and in the Far East. In some cases lead ores are discovered anew in these regions.

The 13th century sources mention the use of lead for church roofs and for seals attached to documents.

The first attempts to start industrial lead production were made at the end of the 17th century by the well-known merchants and industrialists Stroganovs who had found lead ores on the bank of the Tobol in Siberia. It is known that in 1695 the specimens of the ore they discovered were sent to Germany for analysis.

An upsurge in the development of mining and metallurgy was registered in the epoch of Peter I who encouraged the work of miners and prospectors in every way. In 1704 considerable reserves of lead and silver ores were discovered in the Nerchinsk region (Transbaikal area and the first state enterprise was commissioned there in 1708. In the 18th century several deposits of lead, silver and zinc were found in Altai (Zmeinogorsk, Zyryanov sk and other deposits) which led to the construction of a number of new plants. The lead-smelting works in Barnaul turned out the first metal in 1732. In the years that followed Altai came to play a noticeable role in the world mining industry in both the scale and technical standard of production. Many leading specialists of that period worked at Altai plants. Some of them had been invited by the Russian government from the Saxon town of Freiberg even then famous for its Mining Academy. A lead ore deposit discovered by the German mining engineer Philip Ridder in 1786 was named after him (the town that sprang up on the spot also bore his name till 1941 when it was renamed Leninogorsk). By the end of the 18th century the Altai works had put out more than 63000 tons of lead.

In the middle of the 19th century the Caucasus also became one of the centres of silver-lead production. There the Sadon deposit known even in the times of Queen Tamara began to be developed. Later the Alagir silver-lead works was built nearby. It played a prominent role during the Crimean war of 1853-1856.

The construction of the zinc-lead works in Vladikavkaz (today Ordzhonikidze) began in 1898 and was completed in 1909. During the same period the rich lead-zinc ore reserves were being developed in Tetyukhe (the Far East).

On the eve of the First World War most nonferrous metallurgy enterprises were leased to foreign capitalists. The Tetyukhe mines were managed by Germans, the Altai works and mines by the British and those in the Caucasus by Belgians. The ruthless exploitation of the mineral resources had brought lead production onto the verge of collapse. In 1913 Russian factories met only 1.5 per cent of the country’s need in lead.

Under Soviet government a powerful lead industry was set up which not only fully took care of the national economy’s demand for lead, but made it possible to export it. Metallurgists in the Soviet Union and abroad are well familiar with the UKSZK trademark (Ust-Kamenogorsk Lead-Zinc Combine named after V. I. Le- nin). This lead has been registered at the London nonferrous metals stock exchange market as a commercial quality standard (the same honour was accorded to cadmium). The lead works in Chimkent (Kazakhstan) turns out excellent metal as well. This works was the first to introduce the amalgam refining method developed by Kazakh scientists. For the first time in world metallurgy it has become possible to produce super-pure lead: it contains only 0.00001 per cent of impurities. This means that in one ton of this metal it is possible to “scrape up” only one-tenth of a gram of all alien elements taken together. A metal of a quality high as this will always have enough to do in the semiconductor and laser industries.

We could have ended the chapter on lead here, but for one detail we have so far omitted: the origin of its name. The word svinets (Russian for lead) apparently comes from svinka (diminutive for svinya, pig) as lead nuggets used to be called. (As a matter of fact, today they are also called chushki, another word for pig.) But before becoming svinets this metal lived by other names.

Probably you remember the Soviet writer Samuil Marshak’s fairy-tale about a cat which was first called sun, then cloud, then wind, then mouse and finally a cat. Something like that happened to lead too.

If you take a look in Dal’s Explanatory Dictionary of the Russian Language , you will see that the Russian proverb “word is tin” ( slovo — olovo) did not actually mean tin (olovo), but lead (svinets), a heavier, hence more meaningful, metal (word). And the proverb itself is used to describe a word that is weighty, true and trust-worthy. But why all that mystification? Wouldn’t it be simpler to say “word is lead” (slovo— svinets) 1 ! The point is that in the past lead was called tin in Russia. Tin proper appeared later and at first it was mistaken for lead (these metals indeed have something in common). When finally people learned how to distinguish between the two the old name olovo stuck to the new metal and the old one was named svinets.

But that confusion had left its impression on the language. In the Ukrainian a pencil is called olivets or olovets, although pencils had never been made from tin and lead sticks were indeed used in the old times for writing.

These two metals were also confused by the ancient Romans, among others. They called lead “plumbum-nigrum” (black lead) and tin, “plumbum-candium” (white lead). Tin was brought to ancient Rome from Cyprus which Romans called “Candia”.

“Family” ties also connect lead with molybdenum. Translated from the Greek “molybden” means lead. It appears that ancient Greeks confused the minerals of these metals — galenite and molybdenite — and called both “molybdenum”. But when centuries later a new element was obtained from molubdenite it assumed the old Greek name for lead.

Lead became lead in the long run, and now it can feel safe about its name: “a cat was called a cat”.